I went through the same question years ago,

Here's my two cents.

The fastest way to code: Using libraries
The fastest code execution: Using native/vanilla language features & APIs

But, you should also consider the time it takes to learn new libraries/frameworks. Switching between so many frameworks and their documentation is taking a lot of time (we usually don't account for it)

Plus, depending on libraries (like jQuery) too much moves you away from the real magical stuff under the hood.

There is no definite answer for this. It depends on the nature of your work. However, learning the inner-workings of any language is always an investment with an exponential return.

While working with libraries for production, I recommend you to make your own set of libraries. I know it's re-inventing the wheel. But in this path, not only you get better in coding, but you also pick up super-powers to quickly learn other frameworks.

That's what I did for most simple stuff. For example, packed most essential jQuery features I needed to a tiny 1KB library. For complex requirements, using specialized frameworks is obviously more productive.

Plus, check out youmightnotneedjquery.com